I would go along with the advice given. As a first time buyer and with no experience of the subject I would stick with a reputable dealer, as was said it will cost a bit more but you are far less likely to be sold a problem model and will get some guarantee and good legal rights if things go wrong. With a private sale there can be problems and there are a few people out there selling seriously wrong caravans to unsuspecting people. If you buy privately make sure you have a caravan engineer look it over as he should know what to look for
Mentioning a reputable known dealership is a very strong and valid point as there are a few fly by night dealers around to catch the unwary. Also do not forget to ask for the service history of the caravan as that should have been done annually.
When buying privately a ruse is to tell the person that they have other buyers lined up who are willing to pay even more than what the buyer is asking or that the next person will definitely be taking the caravan. Be careful if buying privately to save a few bob as it may cost you more in the long run if something goes wrong. There are many honest sellers out there, but there are always a few chancers who will swear that the caravan does not have any damp.
Enjoy visiting all the dealerships and do not be afraid to ask any questions.